1. Field of the Invention
The invention relates to a carpet pad for use under a carpet.
2. Description of Prior Art
Carpets or rugs are typically installed over a carpet pad that includes a resilient cushion material. The purpose of the pad is to make the carpeted flooring surface feel soft and luxurious to those walking on it. Secondary purposes of carpet pads are to prolong the life of the carpet by dampening the stresses of traffic and to protect the flooring materials under the carpet from liquid spills that penetrate the carpet. A wide variety of materials are employed for such carpet pads at costs in a range nearly as wide as the cost of the carpet or rug they support.
Natural fibrous materials like jute have been used traditionally for carpet padding and continue to be popular in certain applications. However, most carpet installations in the United States now employ foamed polymeric materials. These materials included synthetic latex rubber, natural rubber and polyurethane, all of which are distinguished by their ability to deform and recover. One of cheapest and most common materials used for carpet pad is an agglomeration of foam pieces, usually of polyurethane, called “re-bond”. Re-bond has a cost advantage in that it is formed from recycled foam material.
Most cushion materials used for carpet pads are open structures with an inherent ability to absorb or transmit liquids. As a result, a liquid spilled onto the carpet tends to saturate the carpet pad and pass through the pad to the flooring underneath. In such cases, the liquid is almost impossible to recover completely. Liquid retained in the pad and on the flooring material beneath it may give rise to bacterial growth, causing the pad to emit an unpleasant odor. To avoid damage to the base flooring and to mitigate odor problems it may be necessary to remove and replace the pad.
Moisture retention in the cushion material also presents a problem for moisture passing upwardly from the floor. Most floor surfaces transmit water vapor from locations of higher humidity beneath them, whether from the ground, the basement, or even the room below, and the volume of this moisture is often surprisingly large. It is therefore very important that any water vapor from beneath the floor be able to pass through the carpet pad. That is, the pad should be permeable to moisture vapor. Otherwise, the base flooring may be exposed to condensation moisture, again resulting in mold or bacterial growth and damage.
This ability to transmit water vapor is called “moisture vapor permeability”, or “breathability”, and is measured in terms of moisture vapor transmission rate. The Carpet and Rug Institute, Dalton, Ga., recommends an upper limit rate of moisture vapor transmission through a floor to be 14.6 to 24.4 grams per square meter per twenty-four hours (14.6 to 24.4 gms/m2/24 hours) (3 to 5 lbs./1000 ft2/24 hours) as measured by the calcium chloride vapor emission test (“Test Method for Measuring Moisture Vapor Emission Rate of Concrete Sub-Floor using Calcium Chloride, ASTM-F-1869-98).
To expedite manufacture and to provide a low friction surface that facilitates carpet installation some carpet pads, especially those of re-bond, have a polyolefin film bonded to their upper surface. As long as the film remains intact, it has the tendency to repel liquids. However, the usual reaction of a homeowner to a liquid spill is to rub or to dab the spill energetically in an effort to prevent the liquid passing into the pad. The films typically used in re-bond pads tend to break easily under pressure, probably because of their thin gauge and/or because of lateral stresses in the inherently irregular re-bond structure. As a result, spills onto carpets are forced into the cushion material by pressure imposed on the pad during efforts to spot clean the spill.
While most of the carpet pads of the prior art initially have the capability to resist the intrusion of liquid spills, this liquid impermeability usually fails due to forces imposed during spot cleaning or after normal traffic. Some pads of the prior art, particularly those of closed cell foams or those having thick film layers, can resist liquid spills made on carpets above them, and can do so even during spot cleaning or after a reasonable level of foot traffic. However, these structures are not moisture vapor transmissive and thus they fail to achieve the desirable level of moisture vapor permeability.
U.S. Pat. No. 6,253,526 (Murphy), assigned to the assignee of the present invention, discloses a process for installation of carpet in which the critical properties of breathability and water impermeability are resident in an underlayment that is separate from the padding. While the underlayment is effective in achieving both desired moisture vapor permeability and resistance to spills it requires a separate installation step which is not cost effective and is therefore not widely used.
WO Publication 01/27382 A1 (Murphy), also assigned to the assignee of the present invention, describes an underlayment for a carpet having the desired properties of moisture vapor permeability, liquid impermeability and durability that is maintained under the pressure of cleaning and that would be tolerant of normal foot traffic on the carpet above. However, the structure of this underlayment uses a laminated substrate of fibrous material, which adds to its cost.
U.S. Pat. No. 5,531,849 (Collins) discloses a pad having a smooth polyurethane foam layer disposed between two film layers. Canadian Patent 2,320,471 (Denney) describes an underlayment with a liquid impervious film formed over containment channels to hold spills near the point of introduction and make them easier to recover. However, the durability of both of these pad structures and the ability to retain liquid imperviousness is highly dependent on the thickness of the film layer employed.
In view of the foregoing, it is believed that desirable to provide a pad structure that is simple and economical to manufacture yet provides the desired combination of properties of liquid impermeability, moisture vapor permeability, and durability.